A heating device in a urea preparation machine in the related art is generally installed in a stirring tank, or installed in an ultrapure water tank for heating water which enters the stirring tank in the urea preparation machine and preparing urea solution. Heating modes in the existing technology are limited, in the case of using a lot of the urea solution, the user requirements cannot be satisfied by using the heating modes in the related art, and the production efficiency of the urea solution is reduced.